The first crucial insight is that for some number, a, whose divisors are {1...n,a}:
((a+1)+(a1))((a+1)(a1)) = ((a/n+n)+(a/nn))((a/n+n)(a/nn)) = 4a.
Let x be the smallest number of ways that some number can be written as the difference of 2 squares.
For x>3
Find the smallest number, s, with 2x divisors, or, if smaller, the smallest number with 2x+1 divisors (always a square);
List the 2x proper divisors of s {1,2,.....s/2,s}
Pair the divisors: {s,1}{s/2,2}...{s/n(x),n(x)}; if there is an odd divisor, it must be s^(1/2); ignore it, as it can't be paired.
Now for each pair of squares:
{((s+1)+(s1))*((s+1)(s1)) to ((s/n(x)+ n(x))+(s/n(x)n(x)))*(((s/n(x)+n(x))(s/n(x)n(x)))}
the products will be equal, hence the differences of squares will be equal too; and there will be no smaller s having this property.
Simplifying the first term, the sum of each such pair will be 4s.
Now if x=997, 2x=1994. There is a list of 2000 'Smallest number with exactly n divisors' at A005179 in Sloane. (By comparison, A094191 has only 50 terms.) The entry for x = 1994 is big:
200907863847425122677829696698750339480263402194787551/
395703197819440822085925522967474696027942973398924001/
172041215029722589741067308883174710829525598277573773/
145777954330976645148844919458910211640915369621405942/
161398763726891734353948988944929648209933956622665643/
63305934348670725319760627630081995.
However, x = 1995 has 2x+1 divisors and must be a square: 5852528640000 = 2419200^2. Since this number is compliant with the necessary conditions, multiply by 4 to obtain 23410114560000, which will be the difference between:
(5852528640000+1)^2(58525286400001)^2 and 996 other pairs of squares.
